1. Field of the Invention
The present invention relates generally to an arrangement which exploits scatter-controlled emissions for chemical sensor or taggant arrangements and more specifically to an arrangement which permits an increase in the security of scatter-controlled emissions, and/or which permits a small change in a chemical environment to be detected.
2. Description of the Related Art
Various attempts have been made to develop taggant arrangements. One example of this can be found in U.S. Pat. No. 5,763,891 issued to Yoshinaga, et al. on Jun. 9, 1998. This arrangement is such that an identification mark is formed using a plurality of recording materials having fluorescent characteristics in wavelength regions that almost overlap each other but which are such that the maximum absorbing characteristics of each occurs at different wavelengths. Thus, in order to detect the presence of the unique combination of fluorescing material, it is necessary to sequentially irradiate a target containing these materials with two different light sources, or at least a source, which is capable of sequentially emitting radiation at two different distinct frequencies.
A further problem which is encountered with this arrangement is that the two fluorescing agents that are contained in an ink or the like type of carrier, are arranged to be sensitive to radiation in a near infrared region, and to have absorption spectrums wherein the maximum wavelengths do not overlap each other. This greatly inhibits the use of such materials outdoors or in environments wherein, merely by way of example, heat from hot machinery or objects lying in the hot sun, and/or the sun itself, are apt to produce so much background IR noise as to render such a taggant useful only in special controlled environments.
On the other hand, an example of a sensing arrangement, which utilizes fluorescing materials, is found in U.S. Pat. No. 5,498,549 issued to Nagel et al. on Mar. 12, 1996. This arrangement is direct to sensing the concentration, for example, partial pressure, of a component or analyte of interest, such as oxygen, in a medium, for example, an aqueous-based medium, such as blood. The aim of this arrangement is to provide accurate, reliable and reproducible concentration determinations, and to enable such determinations in spite of signal transmission problems, such as, bent optical fibers, and other operational difficulties which may affect the quality of the signals being transmitted.
Nevertheless, these arrangements are individually limited in their scope of application and the underlying technology cannot be applied to both sensor and taggant arrangements.
The invention centers on the novel emissive properties of high optical gain materials in a high scattering environment. High optical gain materials emit intense and spectrally narrow light that is dependent on the chemical environment in which high gain materials are contained. When two high-gain materials are placed in the same environment, the properties of each emitter will depend on the chemical composition of the surrounding medium. The invention enables the switching or transferring of energy from one emitter to the other when the chemical environment is changed in a specific manner. Thus, a shift in the spectral emissions can be detected, caused and/or predicted.
While this concept can be applied to a wide variety of different technologies, identifying taggants and sensors are two exemplary forms of application. In the case of a taggant, various possibilities are presented. Merely by way of example, it is possible to impregnate a polymer with at least two optically high gain materials which, for the sake of explanation, shall be referred to as emitters, and to form a thread, fiber, particle, film surface or the like with the thus modified polymer. By engineering the polymer to be selectively porous to one or both liquids or gases (or both), it is possible to place an article in a testing device and to irradiate it to the degree that one of the emitters will be excited to a stimulated level and emit photonic energy at a first expected wavelength. By applying a spray (merely by way of example) containing a predetermined analyte or mediating material, the wavelength will, in the case of a genuinely tagged fiber, shift to a second known wavelength. If this shift is ascertained, then the article being examined can be deemed to have been positively identified.
In the same manner a gas xe2x80x9csnifferxe2x80x9d type sensor (for example) can be created in a manner wherein, if the shift from one wavelength to the other is detected, then the presence of a predetermined gas can be ascertained, and a warning, if it is necessary, issued. It should, of course, be appreciated that many and varied variants are possible without deviating from the concept upon which the present invention is based.
More specifically, scatter controlled emission is an optical scattering process that produces stimulated emission from random media with high-gain. The high-gain media for scatter controlled emissions in an embodiment of the invention resides in a mixture of laser dye molecules and sub-micron scatters dispersed in either a liquid or a solid host material. The emission characteristics of this media fall into two categories, weak broadband features under low intensity illumination (which produces spontaneous emission) and intense, narrow band laser-like emission which occurs when the optical excitation source is above a threshold intensity level (which produces stimulated emissions).
In accordance with the present invention, the stimulated emissions from the random media have a markedly higher chemical sensitivity as compared to spontaneous emissions. By way of example, stimulated emission from a methanol solution containing two laser dyes (4-dicyanmethyline-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) and Carbazine 720), in the presence of 1010/cm3 concentration of titanium dioxide particles (sizes ranging from a few micrometers to less than one micrometer), was able to detect parts per million benzylamine (relative to the dye concentration) in the scattering medium.
Another advantage of this invention is the ability to generate small and efficient light sources, which can serve as replacements for more complex and expensive conventional laser systems. This is due to the composition of the random media, which contain both the active laser material and the feedback mechanism (scatterers). A suitable pump source for excitation is however, required.
A first aspect of the invention resides in a photonically excitable arrangement comprising: a first material which is capable of absorbing and emitting photonic energy and which, when sufficiently excited by photonic energy from an external source, emits stimulated radiation in a first narrow wavelength band; a second material which is capable of absorbing and emitting photonic energy; and a mediating material which causes the photonic emission of the first material to be transferred to the second material which is excited to emit stimulated radiation in a second narrow wavelength band at least partially in place of the emission from the first material in the first narrow wavelength band. This arrangement further comprises a host material in which the first and second materials are dispersed, and scattering particles dispersed amongst the first and second materials for scattering emissions from the first material to the second material.
In this arrangement the mediating material is selected to modify the first material and to change at least one of its characteristics to the degree that the photonic radiation which is emitted from the first material under stimulated conditions, is changed to a form wherein it is absorbed by the second material. A laser can be used as the source.
The scattering particles can be selected from, but not limited to, the group consisting essentially of: silicon carbide, diamond, alumina, barium titanate, zinc oxide and titanium dioxide. The first material is selected from, but not limited to, the group consisting essentially of rhodamine green, DCM, coumarin dyes, fluorescein, anthracene dicarboxaldahyde, and napththalene dicarboxaldahyde. On the other hand, the second material is selected from, but not limited to the group consisting essentially of: seminaphthorhodfluor dyes, dimers of cyanine dyes, hydroxypyrene trisulfonic acid, magnesium orange, BODIPY, fluorescein, and carbazine.
In some embodiments the host can be a polymer structure formed to have a predetermined permeability to fluid material into which a mediating material selected from, but not limited to, the group consisting essentially of: nucleic acid, carbon dioxide, a metal ion, aromatic amine, cyanide, and thiol, can introduced.
A second aspect of the invention resides in a sensor arrangement comprising: a source of photonic energy which emits photonic energy of a photonic level sufficient to induce stimulated emissions from irradiated materials; a cell into which the photonic energy from said source is directed, the cell including a host material in which first and second photonically responsive materials, and scattering particles are dispersed, said first photonically responsive material being excited by exposure to photonic energy from said source to emit stimulated photonic energy in a first frequency range, said cell being adapted to have a mediating material introduced thereinto which causes the photonic energy in the first frequency range, to be transmitted to and absorbed by the second photonically responsive material which becomes sufficiently excited to emit photonic energy in a second frequency range; and a photonically responsive device responsive to the stimulated photonic emissions from the cell for determining the frequency or frequency range of the photonic emissions emitted by the cell during excitement by the source of photonic energy.
As in the previous aspect, the source of photonic energy comprises one of a continuous wave and a pulsed laser, while the first material is selected from the group consisting essentially of: rhodamine green, DCM, coumarin dyes, fluorescein, anthracene dicarboxaldahyde, napththalene dicarboxaldahyde; and the second material is selected from the group consisting essentially of: seminaphthorhodfluor dyes, dimers of cyanine dyes, hydroxypyrene trisulfonic, magnesium orange, BODIPY, fluorescein, and carbazine. The photonically responsive device comprises a photometer or a CCD camera.
A third aspect of the invention resides in a sensing method comprising: using a source of photonic energy to irradiate a mixture of first and second photonic excitable materials; sensing a frequency or frequency range of photonic emissions from the mixture; introducing a mediating material into the mixture; and detecting a change in the frequency or frequency range on photonic emissions which occurs due to a presence of the mediating material. In addition to these steps it is within the scope of this aspect to include the steps of: sensing the intensity of photonic emissions from the mixture in the absence of the mediating material; and sensing the intensity of photonic emissions from the mixture in the presence of the mediating material.
This method may further include the steps of: monitoring a decrease in photonic emissions in a first frequency range and a corresponding increase in photonic emissions in a second frequency range which occurs in response to a change in an amount of mediating material introduced into the mixture.
A further aspect of the invention resides in a method of taggant examination comprising the steps of: preparing a mixture of first and second photonically responsive materials, scattering particles and a mediating material, the first and second photonically responsive materials being excited by exposure to photonic energy to respectively emit photonic energy in first and second frequency ranges; incorporating the mixture into a carrier; disposing the carrier with a surface which is to be identified; irradiating the surface with a beam selected to excite the first material to emit stimulated emissions; detecting the frequency at which the stimulated emission occurs; introducing a mediating analyte into the mixture; and detecting a change in frequency which occurs as a result of the introduction of the mediating analyte. This method may further comprise the steps of: sensing the intensity of the stimulated emission at a first frequency prior to introduction of the mediating analyte; sensing the change in intensity with a change in mediating analyte; and sensing the increase of the intensity of the emission at a second frequency as the concentration of the analyte increases.
Another aspect of the invention resides in a taggant comprising: a fluid permeable host material exposable to beam of photonic energy from a source which is remotely located from the host material; first and second photonically responsive materials which are dispersed through the host material; and reflecting particles which are dispersed in the host material with the first and second photonically responsive materials to establish a high optical gain media through which photonic energy can be amplified and reflected back to a remote detector. In this arrangement also, the scattering particles are selected from, but not limited to the group consisting essentially of: silicon carbide, diamond, alumina, and barium titanate, zinc oxide and titanium dioxide.
The host material in this instance can be formed of a fluid permeable polymeric structure.